Wednesday, May 11, 2016

Phytoremediation? Huh

In the middle of a New York Times article about a new 911 call center in New York City, an intriguing comment: 
One answer involves an experiment in phytoremediation, the use of plants to help purify the interior environment, undertaken with Rensselaer Polytechnic Institute. 
Exhaust air from a training room is pumped out through ductwork to a ceiling diffuser in a nearby corridor. As the air falls from the diffuser, it is gently pulled into a grid of permeable planters lining the corridor and carried through the plants’ root systems. These act as a filter. 
The cleaned air is then pumped back to the training room in a relatively closed circuit that will permit architects and engineers to measure the system’s efficacy. Whatever else, it offers a breath of greenery within the mechanical cube.
The article links to a RPI press release about this technique; a brief Google search reveals some NASA  research into using plants to remove indoor VOCs. I guess the question I have is this - do the plants/dirt actually absorb the compounds (decane, etc) or do they metabolize them? Probably the former, I suspect, which may mean the plants/dirt need to be replaced? 

10 comments:

  1. Why can't it be both. Soil has lots of beneficial bacteria that can metabolize any number of compounds. It is pretty established that microbes in the root system are often times necessary for plants with processes such as nitrogen fixation. A likely scenario could be the soil absorbs the compounds and then either the plant or soil microbes metabolize the compounds.

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    1. Gee, I wish I had remembered that dirt has bacteria. (headslap)

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    2. and among them geosmin-producing actinobacteria, responsible for smell of moist dirt. I wonder how the root-like soil scent improves the interior environment

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  2. Choice quote that caught my eye in that NASA document (p 5, emph mine): "A number of low-light tolerant foliage plants were placed into the 'Biohome' and the facility allowed to equilibrate for several days. The striking result was that the symptoms of runny eyes were no longer exhibited, and GC/MS analysis confirmed the reduction of VOCs in the atmosphere. In order to develop a case study for habitation, a graduate student lived in the chamber for the summer, with no negative health effects observed." Hats off to that grad student...

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  3. With all the current hysteria about mold in buildings, I'm surprised that they can use plants and soil as a component of the HVAC system.

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  4. Ah, geosmin. The bane of drinking water suppliers that use surface water. Geosmin is a tertiary alcohol and resists oxidation by chlorine. Most people can smell it in water when its concentration is >10 ng/L. A few (including me) can't smell it at 200 ng/L.

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  5. http://ehp.niehs.nih.gov/15-10037/

    While removing VOC's is important, studies such as the one I have linked are now showing that it is indoor CO2 itself which is likely the bigger problem. Elevated CO2 has long been considered a proxy for "bad air quality" as it correlates with high VOCs, but it is now becoming clear the CO2 itself is part of the "bad", and has significant impacts on human cognition and performance at real-world levels.

    I am surprised the environmental community hasn't picked up on this a bit more, as it has major relevance to the climate change debate. Since indoor CO2 levels tend to be a few hundred ppm or more higher than outdoor levels, many buildings are already at levels which are found to negatively impact people's performance. This will only get worse as we pump more CO2 into the atmosphere. Also it is important to note that a lot proposed "geoengineering" hacks would not do anything about this problem (ditto, ocean acidification).

    CO2 may be "plant food", but equally so, it is "people poison".

    Whose side are you on?

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  6. We've had plants in our organic teaching labs for a couple of years now. I'm pretty sure air purification was the reason, though I always joked that some committee or another had extra funds to spend down at the end of a fiscal year...

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  7. I believe plants, like humans also have a fairly high number of oxidase enzymes that can metabolize, well, certainly decane, which would make them somewhat renewable.

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  8. I believe plants, like humans also have a fairly high number of oxidase enzymes that can metabolize, well, certainly decane, which would make them somewhat renewable.

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